Nothing leaked and there were no injuries in the derailment near the Schuylkill River, which occurred about 1 a.m. EST (0600 GMT), the U.S. Coast Guard said in a statement. CSX Railroad said it would take one to two days for workers to remove the oil and sand cargo and the derailed cars.

The accident was the latest in a series of crashes or derailments of trains carrying crude oil in the United States and Canada that has raised safety concerns.

The Schuylkill Expressway was closed for nearly an hour after the derailment and again at about noon, according to a spokesman for the Pennsylvania Department of Transportation.

Delays occurred as well as motorists slowed to look at a tanker car and a freight car visibly leaning sideways on the railway bridge.

CSX Corp released a statement saying the 101-car freight train was headed to Philadelphia from Chicago, and that seven cars derailed on the bridge.

Six of the derailed cars carried crude oil, CSX was quoted as saying. The cause of the derailment was unknown, and no injuries were reported.

The cars that derailed were at the back of the train, CSX said.

"The investigation continues into the cause of the derailment," it said.

Last July, a runaway oil train derailed and exploded in the centre of the Quebec town of Lac-Megantic, killing 47 people.

In early November, an oil train derailed in rural Alabama and erupted into flames that took several days to extinguish.

On Dec. 30, an oil train collided with a derailed car from a grain train outside the small town of Casselton, North Dakota. The fiery collision spilled more 400,000 gallons of crude and forced the evacuation of 1,400 people from their homes.